1. Field of the Invention
The present invention relates in general to automotive door locks, and particularly, to electric actuators of the door locks, which carry out locking and unlocking operations of the door lock with an aid of electric power.
2. Description of the Prior Art
In order to clarify the task of the present invention, one of conventional electric actuators of the above-mentioned type will be outlined which is disclosed in Japanese Utility Model Second Provisional Publication No. 54-30317.
The electric actuator of the publication is so designed as to drive an operation lever of the door lock by means of both a manual labor and a power produced by an electric motor.
For permitting both the manual operation and electrically powered operation, the actuator has a speed reduction device which comprises a gear driven by an electric motor and a sector gear meshed with the gear, and a lost-motion mechanism which is arranged between the sector gear and the operation lever. A biasing spring is further employed for biasing the lost-motion mechanism toward its neutral position.
With this arrangement, a manual operation of the operation lever via a locking knob is permitted without actuating the speed reduction device and the motor.
However, due to its inherent construction, the conventional electric actuator has the following drawbacks.
That is, the lost-motion stroke of the lost-motion mechanism is considerably large as compared with the effective stroke of the operation lever, which causes a bulky construction of the actuator. Furthermore, employment of the biasing spring makes the actuator complicated in construction.